1. Field of the Invention
The present invention is directed to a method for loading data on a tape, such as a magnetic tape, as well as to a tape for implementing the method, such as a tape having a hole pattern therein.
2. Description of the Prior Art
It is known to write data on a strip-like data carrier, such as a magnetic tape, in a controlled sequence and at controlled locations on the tape by the execution of a bit output program. Typically, data are written in a number of parallel tracks on the tape, the tracks proceeding parallel to the tape transport direction, which is along the longitudinal (longest) direction of the tape. The tape can be transported bidirectionally during the execution of the bit output program so that the data can be written on the tape from one end to the other, while the tape is moving in a first direction, and then the tape movement direction is reversed so that data are written in a parallel track while the tape moves from the second end back to the first end. The first end is usually referred to as the "beginning of tape", or BOT, and the opposite end is referred to as the "end of tape", or EOT.
During the execution of the bit output program, the tape is moved extremely fast, and therefore the tape transport system must have some way of recognizing BOT and EOT, as well as having some kind of indication when either BOT or EOT is approaching. For this purpose, a standardized system of tape holes or tape hole patterns has been devised, which is employed in high speed data reading and writing systems. Accordingly, a BOT marker is provided at one end of a conventional tape, which consists of several pairs, often four pairs, of holes which are spaced along the longitudinal direction of the tape, near the physical beginning edge of the tape. The holes in each pair are substantially vertically aligned in a direction perpendicular to the longitudinal direction. The pairs of holes are respectively designated with numbers, so that if four such pairs are employed, they will be designated BOT1, BOT2, BOT3 and BOT4.
The tape drive is provided with a light barrier system, i.e., a light emitter and a light receiver, so that as the tape passes between the light emitter and light receiver, the presence of the holes is noted and the drive is controlled accordingly.
The tape is also typically provided with a tape identification (tape ID) and/or cartridge identification (cartridge ID) hole pattern between BOT1 and BOT2. This hole pattern provides identification regarding the tape or cartridge itself, such as file information, information about the data to be stored thereon, identification of the tape manufacturer or tape type, or identification regarding a drive or drives with which the tape or cartridge is compatible.
According to the standard, the beginning of tape hole pair designated BOT1 will be the farthest from the physical beginning edge of the tape, and BOT4 will be closest to the physical edge. At some point proceeding in a direction away from the physical beginning of the tape, beyond BOT1, a load point (LP) marker hole will be provided, which is a single hole in the tape that indicates the start of the useable recording area when the tape transport motion is in the direction conventionally designated as the "forward" direction. Data are stored on the tape magnetically only after the load point marker is traversed.
At the opposite end of the tape, a series of single holes is provided in the tape to indicate the end of the tape. These single holes will usually be spaced from the longitudinal edge of the tape at the same distance as one of the holes in the hole pairs identifying the beginning of the tape. If four such end of tape identifiers or markers are employed, they will be designated EOT1, EOT2, EOT3 and EOT4, with EOT4 being closest to the physical end of the tape and EOT1 being farthest from the physical end of the tape. Preceding EOT1, at some point farther from the physical end of the tape than EOT1, is an early warning (EW) marker, which is a hole disposed at approximately the same location from the longitudinal edge of the tape as the load point marker. This hole provides an early indication to the drive of the approaching end of the tape, and is usually the point where writing of data onto the tape ceases when the tape is moving in the forward direction.
For bidirectional loading of data onto a tape, wherein the tape moves rapidly back and forth between the (arbitrarily) designated beginning of tape and end of tape, when the tape moves in a direction opposite to the arbitrarily designated "forward" direction, the early warning marker can then serve as the load point marker to begin loading of data when the tape is moving opposite the forward direction, and the aforementioned load point marker can then serve as the early warning marker to indicate the approaching beginning of the tape and the necessity of undertaking a direction reversal.
In conventional loading systems, as noted above, data loading takes place by starting with a data track, typically near the longitudinal edge of the tape, at the point at which the LP marker after BOT1 is reached, and the tape is transported in the "forward" direction until data loading stops at the early warning point, whereupon a reversal of the tape transport direction takes place and data are then loaded on a parallel track, typically adjacent to the just-written track, as the tape moves back in the opposite direction. Data loading then ceases when the load point marker preceding BOT1 is reached, and a direction reversal again takes place. This sequence is repeated until all tracks on the tape are filled, or until no more data are available for writing onto the tape.
If all of the data stored on a tape are to be read therefrom, the same procedure is repeated with the magnetic head operating in a read mode, rather than a write mode. If only a portion of the data are to be read, or if designated data are to be read, a search program can be undertaken to try to position the tape as quickly as possible to read the desired data without having to sequence through the entirety of the data stored on the tape. Depending on where the tape happens to be positioned on the spools along its longitudinal length, however, a considerable length of tape may have to be traversed before the location is reached at which the desired data are stored. For example, if the tape at the conclusion of a preceding operation happens to be positioned so that a part of the tape close to the beginning of the tape is adjacent the read/write head, but data are desired to be read which are located near the end of the tape, the tape must be transported through virtually its entire length before the data can be accessed. If this occurs multiple times during multiple data access operations, this can result in considerable delays in gaining access to the data, and moreover requires that the tape and tape transport system be operated at a high speed during which no direct benefit is being obtained, i.e., no data are being read.